The present invention relates to electromagnetic vibration generators, sometimes known in the art as shakers, which are employed for the vibration testing of components, apparatus and equipment in numerous branches of industry and research. Such electromagnetic vibration generators basically consist of an armature which is suspended from a rigid body or stator and having a coil carried by the armature located in an air gap in the stator. A D.C. magnetic field is generated across the air gap either by permanent magnets or electromagnets and when an alternating current is fed through the armature coil, the armature is caused to vibrate along its axis at the frequency of the applied alternating current. The armature is mounted on bearings and has a plurality of peripheral suspension members disposed around it which center the armature in the air gap and allow free movement along its axis of vibration but which impose a high stiffness to any lateral movement of the armature normal to its axis of vibration. An article to be vibration tested may be placed directly on top of the armature or on a work table carried by the armature when the vibration testing is to be carried out in the vertical mode, or the article to be tested may be placed on a horizontal slip table coupled to the armature when the vibration testing is to be carried out in the horizontal mode, as is well known in the art.
In one known vibration generator the peripheral suspension members each consist of a flexure member in the form of one or more leaves of polypropylene which are rigidly connected at one end to the armature and anchored at the other end to the stator via a U-shaped bracket. Although such a flexible suspension structure has been found to be adequate when the vibrational stroke of the armature is within certain limits which have hitherto been accepted by users; there is now a requirement for a longer vibrational stroke of the armature. As a result, premature failure of the bracket can occur due to fatigue since it cannot sustain the increased flexing load imposed upon it by the larger vibrational stroke of the armature.